1. Field of the Invention
The present invention relates to a system for controlling the electric power transmitted in a reverse channel in a mobile communication system, and more particularly to a system for controlling the electric power transmitted in a reverse channel when a plurality of radio communication lines are simultaneously connected to a single mobile radio station for a relatively long period of time on a network as upon soft hand-over in a CDMA (Code Division Multiple Access) method.
2. Description of the Related Art
As one conventional system for controlling the electric power transmitted in a reverse channel, there is an invention "Transmitted Electric Power Controlling System" disclosed in Japanese Patent Laid-open publication No. 16149/89. The disclosed system serves to judge accurately the value of transmitted electric power to be controlled in view of the quality of communication lines. The system measures the communication qualities including a reception level, bit error rate, and so forth of individual reverse channels in use with reception level judging circuits, bit error rate judging circuits, and so forth installed in respective base radio stations, and minimizes the value of transmitted electric power of mobile radio stations in use with a transmitted electric power control signal generating circuit or the like for each of the respective communication lines to be controlled individually such that the communication qualities will not drop below range of permitted values.
FIG. 1 of the accompanying drawings shows in block form a circuit arrangement applied to the conventional system for controlling the electric power transmitted in a reverse channel, showing the objects as disclosed in the above publication applied to a mobile communication system.
In FIG. 1, a communication line which transmits from a mobile radio station 11 to a base radio station 21 is referred to as a reverse channel. A signal in the reverse channel is transmitted from a transmitter 12 of the mobile radio station 11 through a transmitting/receiving antenna 14 of the mobile radio station 11 and a transmitting/receiving antenna 22 of the base radio station 21 to a receiver 23 of the base radio station 21, which relays a demodulated signal to an upper-layer station.
The receiver 23 of the base radio station 21 corresponds to a receiver group 1 shown in FIG. 1 of the above publication. The base radio station 21 has a radio communication quality measuring circuit 24 which corresponds to a measuring unit of reception level judging circuit 2 and a measuring unit of bit error rate judging circuit 3 which are shown in FIG. 1 of the above publication. The radio communication quality measuring circuit 24 measures radio communication qualities including the reception level, bit error rate, and so forth of a signal received by the receiver 23 of the base radio station 21. The base radio station 21 also has a reverse channel transmitted electric power control circuit 25 which corresponds to a circuit that is a combination of a judging unit of the reception level judging circuit 2, a judging unit of the bit error rate judging circuit 3, and a transmitted electric power control signal generating circuit 4 which are shown in FIG. 1 of the above publication. The reverse channel transmitted electric power control circuit 25 checks the radio communication qualities measured by the radio communication quality measuring circuit 24 against a permitted range of preset values to judge whether there is still a margin by which the value of transmitted electric power of the mobile radio station 11 can further be reduced. If there is such a margin, then the reverse channel transmitted electric power control circuit 25 sends a command signal through a transmitter 26 and the transmitting/receiving antenna 22 to the mobile radio station 11 to instruct the mobile radio station 11 to reduce the value of reverse channel transmitted electric power thereof. The transmitter 26 corresponds to a transmitter 5 shown in FIG. 1 of the above publication.
The mobile radio station 11 has a transmitted electric power control circuit 13. When the transmitted electric power control circuit 13 receives a command signal to reduce the reverse channel transmitted electric power transmitted from the reverse channel transmitted electric power control circuit 25 through the transmitting/receiving antenna 14 and a receiver 15, the transmitted electric power control circuit 13 reduces the value of transmitted electric power of the transmitter 12.
One problem of the conventional system shown in FIG. 1 of the accompanying drawings is that when a plurality of radio channels are connected for a relatively long period of time and signals of all reverse channels are selectively combined and relayed to a upper-layer station as upon no-break soft hand-over, it is not possible to achieve a maximum effect for reducing the value of electric power transmitted in reverse channels of the mobile radio stations with only the conventional reverse channel transmitted electric power control process.
The reasons for the above drawbacks are as follows: In a base station control station which connects a plurality of radio communication lines, the communication qualities of reverse channels which have been selectively combined are higher than the communication qualities of individual communication lines. However, according to the conventional reverse channel transmitted electric power control process, the base station control station, which connects a selectively combined plurality of radio communication lines, has no communication quality measuring functions to measure the communication qualities of reverse channels which have been selectively combined and also no abilities to reflect those communication qualities in the control of the value of transmitted electric power in the reverse channels of the respective base radio stations. Here, selectively combined connecting means bringing together into one channel those communication lines which have been connected to one mobile radio station through a plurality of mobile base stations by base station control station.